His intellectual ties are with the old Frankfurt School and the cantankerous philosopher Theodor Adorno. His idiosyncratic music, which explores sound, is not, in America, in fashion and is little known here. A rare recent appearance by Lachenmann at an equally rare program of his grating, challenging, the-status-is-never-quo music in the Big Apple did not attract attention.

This week, Monday Evening Concerts devoted its evening to Lachenmann. Visiting Los Angeles for the first time, he was on hand as pianist. An ensemble of young musicians repeated its performance of a major work from 1984 that made so few waves at its New York concert. Three members of a second group, the Ensemble Recherche, flew in from Germany to play really difficult music written 20 years ago.

The concert was a sensation. Empty seats were hard to find at the Colburn School's Zipper Concert Hall. A buzz was in the air. Members of the L.A. music elite, including composers from the academic and film worlds, were on hand. The audience stood and applauded lustily. More than once.

Lachenmann's situation is a curious one. He remains devoted to making music in new ways at a time when what is new is said to have become old. Many of his favorite techniques -- the rasping of bows against the bridge of a violin or cello, the tapping on the tops of clarinets with their mouthpieces removed, the clicking of flute keys, the blowing of wind instruments into a piano to make the strings resonate -- are things the avant-garde has been up to for decades.

What Lachenmann brings to the experimental table is a captivating sense of quest. He achieves an unusually sharp focus. He operates just at the edge of tradition. The result is music that sounds remarkably fresh, that is quite mysterious yet readily engages the ear.

Monday's concert was an adventure. It began with baby steps. Lachenmann performed his early (1963) "Wiegenmusik" (Cradle Music), which feels more like fragments of sound than the real thing, as a prelude to "Ein Kinderspiel" (Child's Play), written as musical games for his children in 1980. For all his seriousness, Lachenmann has a terrific sense of fun. The English translation of one movement of "Child's Play" is "Fake Chinese (slightly drunk)." He obsesses on such nonsense as tripping down the scale or getting hung up on a repeated chord while toying with its dying resonances.

"Mouvement ( -- vor der Erstarrung)," or "Movement ( -- Before Paralysis)," was played by the Argento Chamber Ensemble conducted by Michel Galante. This was the work in 1984 that contributed to Lachenmann's international recognition as not just an earnest avant-gardist doing funny things to instruments but a visionary who put all those funny things together with brilliant dramatic conviction.

The ensemble is a strange one: Clarinets, violins and percussion come in threes; flutes, trumpets, violas and cellos are in pairs; the bass is the only single. Everyone does something unusual, and a kind of sonic jungle is evoked, the sounds resembling animals and nature communicating in languages you don't understand but still realize are languages.

"Allegro Sostenuto," which was the big work after intermission, is for clarinet, cello and piano, and it received a gripping performance from Shizuyo Oka, Asa Akerberg and Jean-Pierre Collot. The composer describes the work as containing six sections that flow together. His notes almost make it sound like normal music, with an introductory section, an allegro, an appassionato climax, etc. Near the end, clarinet and cello are said to project "normal" notes over piano clusters.

Well, by the end, after so much alluringly odd activity, nothing seems normal. Unlike the percussive extravaganza of "Mouvement," Lachenmann here goes inside individual instrumental sounds while constantly transforming their sonorities. Your ears are never on solid ground.

This program was the last of this season's Monday Evening Concerts. Two years ago, the venerable new music series parted ways with the Los Angeles County Museum of Art. Both institutions have spectacularly reinvented themselves since. But only the one that gave a concert Monday has done so without naysayers.